Various types of carbamate pesticides have been previously described. For example, U.S. Pat. No. 3,997,549 to Fukuto and Black discloses N-arylsulfenylated derivatives of benzofuranyl methylcarbamates as effective pesticides; U.S. Pat. No. 4,006,231 to Black and Fukuto discloses N-aminosulfenylated derivatives of carbofuran as effective pesticides; and U.S. Pat. No. 3,843,689 to Brown et al. discloses the production of N-methyl-N-phenyldithiocarbamate from the N-chlorothiocarbamates (i.e. N-chlorosulfenylcarbamate).
Further with regard to the last-mentioned patent, Brown et al. refer in rather broad-brush fashion to the reaction of N-chlorosulfenylcarbamates with a wide variety of substituents, including alcohols, mercaptans, ureas, carbamates, amines, amides, anilides, and other compounds that have active hydrogen atoms to give the corresponding substitution product and hydrochloric acid by reaction with the sulfenyl halide component of the compound. Brown et al. do not appear to have actually performed some of the reactions, for example, with alcohol, inasmuch as details of processing to yield a useful product are not given.
In accordance with the present invention, a novel class of carbamate ester compounds are provided, which are effective pesticides. The carbamate compounds are derived in accordance with one of several reaction routes, one of which involves the reaction of an N-chlorosulfenylcarbamate ester. However, in contrast with the simple chemistry envisioned by the Brown et al. U.S. Pat. No. 3,843,689, we have discovered that a sulfur-polymerizing reaction occurs when pyridine or other suitable base is used as a hydrogen chloride acceptor. We have further found that in order to prepare the resultant alkoxy compound substantially free from polysulfide compounds, one has to resort either to significant purification steps or to other methods of preparation.
More particularly, the novel carbamate ester compounds are useful as insecticides and are prepared by following one of three different methods: (a) N-(dialkylaminosulfenyl)carbamate ester with an alcohol in a suitable organic solvent in the presence of an acid such as acetic acid; (b) as above described, reacting an N-chlorosulfenylcarbamate ester with an alcohol in a suitable organic solvent in the presence of a hydrogen chloride acceptor such as pyridine or other suitable base; and (c) reacting an N-chlorosulfenylcarbamate with a metal alcoholate in a suitable organic solvent. Only in the first embodiment are the products of the reaction substantially free from polymeric sulfur compounds. In the other embodiments, unpurified carbamates are formed containing a substantial amount, about 5 to about 40 weight percent, of the corresponding polysulfide compound. In order to prepare an N-chlorosulfenylcarbamate ester, from a carbamate ester, sulfur dichloride is usually used. However, sulfur monochloride can be used instead of sulfur dichloride, resulting in a final product which, contains larger amounts of polysulfide derivatives. Although not readily susceptible to easy explanation, it appears that the polysulfide compound has certain advantages over the purified compound in that it has been found to be substantially as effective as an insecticide as the purified compound on a weight basis against insects, but to have decreased toxicity on a weight basis against mammals. While it is not desired to be limited to any particular theory, it can be hypothesized that the polysulfide component of the compound serves to facilitate the incorporation, or metabolism, of the compound in insects while not having that effect in mammals; therefore, in mammals the polysulfide component of the compound serves simply as a diluent. The result is an insecticide which is not only inexpensive because of the lack of need for extraordinary purification steps but also because of the fact that the costly components of the molecules, e.g., the furan components, are present in a relatively smaller percentage of the final formulation than is the case with the pure compound. In either case, the compounds are found to have substantially reduced mammalian toxicity, e.g. as compared with other potent insecticides such as carbofuran, described in U.S. Pat. No. 3,474,171.